Clinical cases
Tumour lysis syndrome: a case-based approach
This is an illustrative educational case — not a real patient. Tumour lysis syndrome is a serious emergency that can happen when large numbers of cancer cells break down very quickly, usually just after starting treatment. As the cells burst, they spill chemicals into the blood faster than the kidneys can clear them, which can upset the heart rhythm and damage the kidneys. This case explains how it presents, why it is dangerous, who is most at risk, and how cancer teams prevent and treat it. It is general education for people affected by cancer and their families, not personal medical advice — always follow your own oncology team's guidance.
Education and reference only. This article explains how treatments work in plain language — it contains no doses and is not a substitute for advice from your doctor or pharmacist. Always discuss your own treatment with a qualified clinician.
The presentation
Imagine someone who has just started treatment for a fast-growing blood cancer, such as a leukaemia or lymphoma. Within a day or two they begin to feel unwell in vague but worrying ways: nausea and vomiting, tiredness, muscle cramps or twitching, tingling around the mouth or in the fingers, and passing less urine than usual. Some notice a racing or irregular heartbeat, and in severe cases there can be confusion, fits or collapse. These symptoms come from the sudden shift in blood chemistry as tumour cells break apart. Because the changes can be silent at first and are picked up on blood tests before symptoms appear, hospital teams monitor high-risk patients closely. For patients and families, the key is to report any new symptoms promptly rather than waiting to see if they pass.
Why it happens and why it is dangerous
When cancer cells die, they release their contents — including potassium, phosphate and a substance called uric acid — into the bloodstream. If a huge number of cells die at once, as can happen when a bulky, fast-growing cancer responds quickly to treatment, these chemicals build up faster than the kidneys can remove them. High potassium can trigger dangerous, even fatal, heart rhythm problems. High phosphate pulls down calcium, causing cramps, twitching and fits. Uric acid and phosphate can crystallise in the kidneys, blocking them and causing acute kidney injury, which in turn makes every other problem worse. This dangerous spiral is why tumour lysis syndrome is treated as an emergency, and why prevention before and during treatment is such an important part of cancer care.
How teams prevent and treat it
Cancer teams work hard to stop tumour lysis syndrome before it starts. People judged to be at higher risk are given plenty of fluids, usually into a vein, to keep urine flowing and flush the chemicals through the kidneys. Medicines are used to lower uric acid — one type reduces how much is made, and another, more powerful drug can break uric acid down rapidly in high-risk cases. Blood tests are checked frequently, sometimes several times a day, so that rising potassium, phosphate or uric acid is caught early. If levels climb dangerously or the kidneys struggle, treatment is stepped up, and in the most severe cases dialysis is used to clean the blood. Heart tracing may be used to watch for rhythm changes from high potassium. All of this is delivered under specialist supervision in hospital.
Who is more at risk
The main risk comes from having a large amount of cancer that grows and responds to treatment quickly. Certain blood cancers, such as some aggressive lymphomas and leukaemias, carry the highest risk, especially when the disease is bulky or the white cell count is very high. The risk is greatest in the first few days after starting chemotherapy or other cancer treatments, though it can occasionally happen before treatment or with newer targeted therapies. People who already have reduced kidney function, who are dehydrated, or whose blood tests are abnormal at the start are more vulnerable. Because these risks are well recognised, oncology teams assess every patient's risk before treatment and put prevention in place for those who need it. Patients do not have to work this out themselves — but knowing the risk exists helps them report symptoms early.
The safe pathway
For anyone having cancer treatment, the safe pathway is to know the warning signs and act on them quickly. If you or a relative on treatment develop new muscle cramps, twitching, tingling, a racing or irregular heartbeat, are passing much less urine, or feel newly confused or very unwell, contact your cancer team's advice line straight away — hospitals give oncology patients a 24-hour number for exactly this. If someone collapses, has a seizure, or has severe chest pain or breathing difficulty, call 999. Do not wait to see if symptoms settle and do not assume they are just side effects. Tumour lysis syndrome is a recognised, largely preventable emergency, and speaking up early lets the team check bloods and act before things become dangerous. Always follow the specific instructions your own team has given you.
In short
Key takeaways
- Tumour lysis syndrome happens when many cancer cells break down at once, flooding the blood with chemicals, usually soon after starting treatment.
- It can cause dangerous heart rhythm problems, muscle cramps and fits, and can damage the kidneys.
- The highest risk is with bulky, fast-growing blood cancers in the first days of chemotherapy.
- Cancer teams prevent it with fluids, uric-acid-lowering medicines and frequent blood tests, and treat severe cases in hospital.
- This is general education only — report new symptoms to your cancer advice line urgently, and call 999 for collapse, seizure or severe breathing problems.
Answers
Frequently asked questions
Who needs to worry about tumour lysis syndrome?
It mainly affects people being treated for bulky, fast-growing blood cancers such as some leukaemias and lymphomas, especially in the first few days of treatment. Your cancer team assesses everyone's risk before starting and puts prevention in place if needed. If you are on cancer treatment, you do not need to work out your own risk, but it helps to know the warning signs and to report any new symptoms promptly.
What symptoms should make me contact my cancer team urgently?
Contact your team's 24-hour advice line straight away if you develop new muscle cramps, twitching, tingling around the mouth or fingers, a racing or irregular heartbeat, are passing much less urine than usual, or feel newly confused, sick or very unwell after starting treatment. These can be signs of the blood-chemistry changes seen in tumour lysis syndrome, which are treatable when caught early.
When is it a 999 emergency?
Call 999 if someone on cancer treatment collapses, has a seizure, develops severe chest pain, has a very irregular or racing heartbeat with faintness, or has serious difficulty breathing. These can be signs of a dangerous heart rhythm or other severe complication. For less severe but new symptoms, ring your cancer team's urgent advice line rather than waiting — this is exactly what the line is for.
Go deeper
Related guides
Sources
Where this is drawn from
- National Institute for Health and Care Excellence (NICE). Clinical Knowledge Summaries and haematological cancers guidance. 2023.
- British Committee for Standards in Haematology (BSH). Guidelines on the management of tumour lysis syndrome. 2022.
- NHS. Chemotherapy: side effects and when to get urgent advice. 2024.
Need clear, evidence-led health content?
We write accurate, dose-free patient information and medicines content for teams.